Content Warning: This article contains minor spoilers for The Flash season 7.
Apart from dabbling in time travel occasionally, both to the past and the future, The Flash is popularly known for foreshadowing major events as well. Although sometimes the foreshadowing is blatantly obvious, like the outright mention of a future villain, sometimes it's subtle enough to miss until the actual payoff.
Throughout the series, there have been moments that were foreshadowed even as far back as the pilot episode, only to happen several seasons later. Although some things haven't happened yet, there are several moments and quotes that were initially dismissed until the major event they foreshadowed happened, bringing everything full circle.
Barry Going To Jail
The season 1 finale, "Fast Enough" had Barry running back in time, leading to some speed force visions. Among them was a vision of Barry handcuffed and wearing a prison jumpsuit. Later in the first episode of season 4, Barry came out of the speed force, saying random things, one of which was, "Your Honor, I'm innocent. I didn't do this. I didn't kill anyone."
The vision and seemingly random quote finally came into play in the season 4 episode, "Don't Run," when Barry was arrested for Devoe's murder and subsequently tried in court. Based on this and the other gibberish Barry said, it seems he was saying things related to his past and future, which he likely saw while trapped in the speed force.
Caitlyn Becoming Killer Frost
Another key moment from Barry's speed force visions in the season 1 finale was the one of Caitlyn as Killer Frost. The vision simply showed Caitlyn with part of her hair looking white and her hand stretched out.
This particular foreshadowing seemed to apply to more than just Caitlyn becoming Killer Frost as Barry, Cisco and Harry met a Killer Frost on Earth 2 during season 2. The Caitlyn from Earth 1 fought against the transition for a while when she discovered she had cryokinetic powers, but eventually failed to suppress them in season 3, making the vision a reality.
Savitar's Identity
Besides the consequences of Flashpoint, a major aspect of season 3 was the villain Savitar. Barry and Team Flash spent most of the season trying to figure out his identity. In the episode "I Know Who You Are," Savitar's identity was finally revealed, showing him to be a time remnant of Barry from the future.
Once his identity was revealed, some things Savitar said prior to the reveal were seen in a new light. From Savitar's infamous "I am the future, Flash" versus "I am the future Flash" quote that had the fandom divided to little hints Savitar gave of his backstory, such as telling Barry he was there at the time of his creation. One other subtle hint that foreshadowed the big reveal was Savitar making reference to something Reverb—Vibe's alternate from Earth 2—said, which only Barry and Cisco knew.
Iris Marrying Barry
Before Iris and Barry got together, both of them were with other people. Iris was with Eddie and Barry was with Patty Spivot for part of season 2. But, it was no secret that Barry had feelings for Iris and after Eddie's death and Patty leaving, the two eventually started dating and got married in season 4, leading to her becoming Iris West-Allen.
The double-barrel surname was shown as far back as season 1 with the article that spoke of the Flash vanishing during a crisis. The by-line of the article read "by Iris West-Allen" showing that sometime before that dreadful future came to , the two of them would be married. It influenced several events, including Eddie's death when he sacrificed himself to get rid of Reverse-Flash, knowing Iris was fated to be with Barry anyway.
The Villain Devoe
One of the most powerful villains on The Flash was Devoe, whose appearance in season 4 was foreshadowed in season 3 through comments made by other villains. Abra Kadabra mentioned him while listing some of Barry's worst rivals in the episode "Abra Kadabra." Savitar also mentioned Devoe in "Finish Line" with reference to the cerebral inhibitor built in the future to stop him.
Devoe was only one out of a few villains foreshadowed on the show before he appeared, the others being Godspeed and Red Death—the latter of which is yet to appear. Most times, villain foreshadowing doesn't give away too many details about the actual villain, but the fact that Devoe was mentioned prior to his appearance showed how big of an impact he was going to have.
Nora ing Team Flash
During season 4, an unknown young lady kept popping up and interacting with of Team Flash. She was at Barry and Iris' wedding, then showed up twice at Jitters, and also at Joe and Cecile's home. She finally revealed that she was Nora West-Allen—Barry and Iris's daughter from the future.
The reveal brought one of the quotes from Barry's post-speed force babble back into focus, which was "Nora shouldn't be here." At the time it was easy to dismiss it as gibberish or as something related to his mother, Nora, but in light of the reveal and considering the repercussions of people time-traveling from the future, it seems the line foreshadowed Nora's arrival.
The Flash Vanishing In Crisis
The Crisis On Infinite Earths was foreshadowed as early on in the show as season 1 through an article dated 2024 with a headline about the flash vanishing during a crisis. Due to the setting in of a new timeline after the events of season 5, the crisis moved up to the year 2019 and the actual crisis happened in season 6.
Barry's foreshadowed disappearance cast a dark cloud on Team Flash in the episodes leading up to the crisis, as they all had to prepare to carry on without him. Although the Flash who ended up vanishing in the crisis was Earth-90 Flash instead of Barry, which was different from the events of the comic book The Flash is based on, the sentiment still stands as a Flash did vanish into thin air in the crisis.
The Godspeed Clones
In a flashback that showed the future timeline where Nora was from, she met and fought against Godspeed. Later in season 6, episode 1, "Into The Void," a number of Godspeeds showed up but they weren't the real deal and most of them couldn't speak properly. Fast forward to season 7, Godspeed became a major villain towards the end—and not just Godspeed, but a whole bunch of his clones.
The first Godspeed clones from season 6 were taken as decoys sent by the real one and in hindsight, they seemed to tease the appearance of the real villain not too far in the future along with his many iterations. The appearance of the clones brought things full circle and finally explained their purpose and mission, paving way for the real Godspeed.
"We're Gonna Need More Diapers."
When Nora vanished from the timeline in the season 5 finale, Barry and Iris were comforted by the fact that they were likely going to see her again in the future. In season 7, they started trying for a baby, and later in the season, Nora came back again from the future in one of the most The Flash, but she wasn't the only one of their children who came.
Although the line "We're gonna need more diapers," hasn't been said by anyone else after Barry said it when he came out of the speed force, the events of season 7 brought up theories that it might have been a reference to Barry and Iris having two children instead of one as they'd expected.